travis: Pin to specific minikube version

Workaround for kubernetes/minikube#2704

Resolves: kubevirt#42

Signed-off-by: Fabian Deutsch <fabiand@fedoraproject.org>

.travis.yml

@@ -1,7 +1,7 @@
 sudo: required
 
 env:
-- CHANGE_MINIKUBE_NONE_USER=true K8S_VER=1.9.0 K6T_VER=0.3.0
+- CHANGE_MINIKUBE_NONE_USER=true K8S_VER=1.9.0 K6T_VER=0.3.0 M6E_VER=v0.25.2
 
 notifications:
   irc:
@@ -13,7 +13,7 @@ notifications:
 before_script:
 # Setup minikube
 - curl -Lo kubectl https://storage.googleapis.com/kubernetes-release/release/v$K8S_VER/bin/linux/amd64/kubectl && chmod +x kubectl && sudo mv kubectl /usr/local/bin/
-- curl -Lo minikube https://storage.googleapis.com/minikube/releases/latest/minikube-linux-amd64 && chmod +x minikube && sudo mv minikube /usr/local/bin/
+- curl -Lo minikube https://storage.googleapis.com/minikube/releases/$M6E_VER/minikube-linux-amd64 && chmod +x minikube && sudo mv minikube /usr/local/bin/
 
 - sudo minikube start --vm-driver=none --kubernetes-version=v$K8S_VER
 - minikube update-context